Bio

Digestion - Begins the digestion of carbohydrates

Stomach - Begins the digestion of protein; small molecules such as alcohol absorbed
Small intestine (duodenum) - Continues the digestion of carbohydrate and protein;
begins the digestion of lipids
Small intestine (ilenum) - Completes the digestion of carbohydrates and proteins
into single sugars and amino acids; absorption of single sugars, amino acids and
fatty acids and glycerol
Large intestine - Absorption of water; egestion of undigested food
Digestive enzymes are used to break down food in the gut into small, soluble
molecules that can be absorbed through the gut wall
The surface of the small intestine wall is folded, and has projections called
villi. Villi is the plural of villus.
The epithelial cells that cover each villus themselves have projections called
microvilli
Most of the digested food passes through the epithelial cells of the gut wall and
is carried by blood to the liver.
Digested lipids pass through the gut wall and enter the lacteals.
The lacteals in each villus join together into larger vessels. Then all the
digested lipids pass through a duct into the bloodstream.

The different pHs under investigation will be produced using buffer solutions
Buffer solutions produce a particular pH, and will maintain it if other substances
are added. The amylase will break down the starch. A series of test tubes
containing a mixture of starch and amylase is set up at different pHs. A sample is
removed from the test tubes every 10 seconds to test for the presence of starch.
Iodine solution will turn a blue/black colour when starch is present, so when all
the starch is broken down, a blue-black colour is no longer produced. The iodine
solution will remain orange-brown. A control experiment must be set up – without
the amylase – to make sure that the starch would not break down anyway. The result
of the control experiment must be negative – the colour must remain blue-black –
for results with the enzyme to be valid. When the starch solution is added: start
timing immediately, remove a sample immediately, and test it with iodine solution,
sample the starch-amylase mixture continuously, for example every 10 seconds. For
each pH investigated, record the time taken for the disappearance of starch, ie
when the iodine solution in the spotting tile remains orange-brown. The time taken
for the disappearance of starch is not the rate of reaction. It will give us an
indication of the rate, but is the inverse of the rate – the shorter the time
taken, the greater the rate of the reaction. We can calculate the rate of the
reaction by calculating 1/t, obtaining a measure of the rate of reaction by
dividing one by the time taken for the reaction to occur.

The liver produces bile. Bile emulsifies lipids, breaking them up physically into
tiny droplets. Tiny droplets have a much larger surface area, over which lipases
can work, than larger pieces, or drops of lipid. Contains sodium hydrogencarbonate,
which is an alkali. It neutralises stomach acid and produces the optimum pH for
pancreatic enzymes. Is produced in the liver, but stored and concentrated in the
gall bladder. Carbohydrates - Source of energy, glucose is the main respiratory
substrate. Proteins - Growth and repair. Lipids - Energy, make up part of cell
membranes so essential for normal growth. Digestive enzymes are substances that
help you digest your food. They are secreted (released) by the salivary glands and
cells lining the stomach, pancreas, and small intestine. There are several
digestive enzymes, including amylase, maltase, lactase, lipase, sucrase, and
proteases. Amylase (made in the mouth and pancreas; breaks down complex
carbohydrates) Lipase (made in the pancreas; breaks down fats) Protease (made in
the pancreas; breaks down proteins). In an organism, the active site of each enzyme
is a different shape. It is a perfect match to the shape of the substrate molecule,
or molecules. This is essential to the enzyme being able to work. One enzyme is
therefore specific to one substrate's chemical reaction, or type of chemical
reaction. This theory for the way in which enzymes work is called the lock and key
theory. At low temperatures, the number of successful collisions between the enzyme
and substrate is reduced because their molecular movement decreases. The reaction
is slow. The human body is maintained at 37°C as this is the temperature at which
the enzymes in our body work best. This is not true of the enzymes in all
organisms. Higher temperatures disrupt the shape of the active site, which will
reduce its activity, or prevent it from working. The enzyme will have been
denatured. Denatured - To change the shape of an enzyme's active site, for example
because of high temperatures or extremes of pH. Denatured enzymes no longer work.
Proteins are chains of amino acids joined end to end. This chain is not straight –
it twists and folds as different amino acids in the chain are attracted to, or
repel each other. Each enzyme is made from proteins made of these twisting and
folding amino acids, and therefore the enzyme has a unique shape. This structure is
held together by weak forces between the amino acid molecules in the chain. High
temperatures will break these forces. The enzyme, including its active site, will
change shape and the substrate will no longer fit. The rate of reaction will be
affected, or the reaction will stop. Enzymes are also sensitive to pH. Changing the
pH of its surroundings will also change the shape of the active site of an enzyme.
Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule,
positively and negatively charged amino acid will attract. This contributes to the
folding of the enzyme molecule, its shape, and the shape of the active site.
Changing the pH will affect the charges on the amino acid molecules. Amino acids
that attracted each other may no longer. Again, the shape of the enzyme, along with
its active site, will change. Extremes of pH also denature enzymes. The changes are
usually permanent. Enzymes work inside and outside cells, for instance in the
digestive system where cell pH is kept at 7.0 to 7.4. Cellular enzymes will work
best within this pH range. Different parts of the digestive system produce
different enzymes. These have different optimum pHs. The optimum pH in the stomach
is produced by the secretion of hydrochloric acid. The optimum pH in the duodenum
is produced by the secretion of sodium hydrogencarbonate. Carbohydrases break down
carbohydrates. Starch is a type of carbohydrate. The carbohydrase that breaks down
starch is amylase. Proteases break down proteins. Lipases break down lipids.